Nonaqueous electrolyte secondary batteries such as lithium ion secondary batteries have been already put to practical use as batteries for laptop computers, cellular phones and the like because of their advantages of high energy density, small self-discharge, excellent long-term reliability and the like. In recent years, however, electronic devices have become more sophisticated and the use of batteries in electric vehicles has been expanded, and therefore, there is a demand for development of a secondary battery having a higher energy density.
In such a nonaqueous electrolyte secondary battery, a chemical reaction or decomposition of an electrolyte layer may occur on an electrode surface of a positive electrode and/or a negative electrode. As a result, there arise problems of degradation in the storage characteristic of a battery at a high temperature, degradation of the cycle characteristic of a secondary battery, and generation of a gas from a decomposition product. In order to prevent these problems from occurring, a compound having a function to form a protective coating is added to an electrolyte solution contained in an electrolyte layer. Specifically, when decomposition of the compound added to the electrolyte solution is intentionally accelerated on the surface of a negative electrode active material at the time of initial charge, the thus generated decomposition product forms a protective coating having a protective function, namely, an SEI (Solid Electrolyte Interface), to prevent further decomposition of the electrolyte layer. It has been reported that when the protective coating is thus formed, the chemical reaction or decomposition of the electrolyte layer otherwise occurring on the surface of the negative electrode can be suitably suppressed, and that as a result, an effect of retaining the battery performance of the secondary battery is exhibited.
As an additive for forming a protective coating, use of an oxygen-containing aliphatic compound having alkynyl group and/or alkynylene group (Patent Literature 1), acetylene dicarboxylic ester (Patent Literature 2), 2,4-Hexadienedioic acid dimethyl ester and the like, and vinylene carbonate and/or 1,3-propane sultone (Patent Literature 3), or LiBF4 and acetylene dicarboxylic diester (Patent Literature 4) has been disclosed.
On the other hand, since a secondary battery using conventional graphite-based negative electrode materials have such insufficient capacities that required performances are difficult to attain, investigation utilizing a metal-based negative electrode material, such as silicon or a silicon oxide, as a negative electrode active material have also been made in order to obtain a secondary battery having a high capacity and a high energy density (Patent Literature 5).